$ \left(\dfrac{1}{256}\right)^{\frac{1}{4}}$
Figure out what goes in the blank: $\Big(? \Big)^{4}=\dfrac{1}{256}$ Figure out what goes in the blank: $\Big({\dfrac{1}{4}}\Big)^{4}=\dfrac{1}{256}$ So $\left(\dfrac{1}{256}\right)^{\frac{1}{4}}=\dfrac{1}{4}$